1. Field of the Invention
This invention relates to the treatment and upgrading of bitumen asphaltenes from oil sands. More particularly, whole bitumen recovered from tar sands is deasphalted and the asphaltene portion treated with superheated water.
2. Description of the Related Art
Conventional processing of tar sands involves separating whole bitumen from the oil-bearing sand by treatment with hot water, steam or some combination thereof. The separated whole bitumen is highly viscous and can be transferred by pipeline only if the viscosity is reduced, e.g., as by the addition of a diluent solvent. Whole bitumen can be further processed and upgraded, e.g., fractionation by thermal treatment to remove lighter ends or extraction with a deasphalting solvent to yield a deasphalted oil and an asphaltene precipitate. Either method results in substantial amounts of heavy resid or asphaltene residue which on further processing form coke-like material which cannot be economically converted to useful products and therefore presents disposal problems.
Extraction of tar sands and removal of organics from oil shales has also been accomplished using "supercritical water", i.e., water that is maintained at temperatures above its critical temperature. Since the critical temperature of a material is that temperature above which it cannot be liquified no matter how much pressure is applied, "supercritical water" is a dense fluid. Supercritical fluids are known to possess unusual solvent properties, and their application to separation of organic matter from oil shale and tar sands in the presence of a sulfur-resistant catalyst results in recovered hydrocarbon.
In another approach, whole bitumen treated with "supercritical water" in the presence of CO results in less coke produced via the thermal decomposition route at such elevated temperatures.
At temperatures near or above the critical temperatures, tar sands and whole extracted bitumen undergo undesirable thermal reactions leading to coke formation. Conventional processing of whole bitumen by vacuum distillation or solvent extraction results in a lighter fraction which can be further processed and a significant amount of heavy, solid asphaltene which cannot be economically converted to lighter fractions and thus presents disposal problems as well as loss of potentially valuable hydrocarbon material.